The present invention relates to a method of manufacturing an electronic component to be used in various electronic appliances, and more particularly to a method of manufacturing an electronic component manufactured by intaglio printing.
Recently, electronic appliances are reduced in size, and hence electronic components used in such electronic appliances are also promoted in downsizing. In such background, the conductor patterns of electronic components are requested to be finer in the conductor lines (hereinafter lines for short) for composing patterns, greater in the film thickness of conductor film for composing the conductor patterns for lowering the line resistance, and laminated in structure for reducing the size.
Conductor patterns of conventional electronic components were formed by printing patterns of conductive paste such as silver paste and copper paste on a substrate as a forming object by printing method such as screen printing and intaglio printing, and firing it. For example, as an application of intaglio printing method, in a printing method as disclosed in Japanese Laid-open Patent Publication No. 4-240792, the intaglio corresponding to the conductor pattern to be formed is filled with conductive paste (organic metal ink), the conductive paste is dried and cured, and the pattern is transferred onto the forming object of substrate through a setting resin, so that the desired conductor pattern is formed.
Moreover, in the hybrid IC, thermal head or transparent electrode, since the width of each line and line interval in the conductor pattern are very small, the method making use of thin film forming and etching is often employed. In this method, first, a thin film of conductive material such as gold, aluminum, and ITO (indium tin oxide) is formed on the substrate by vapor deposition or sputtering, and successively a mask pattern corresponding to a desired conductor pattern is formed by photolithography using a photosensitive resin. Consequently, etching the thin film of conductor material by using etchant and mask pattern, the photo-sensitive resin is finally removed, and the conductor pattern is formed.
In such conventional manufacturing method, however, the following problems are involved.
First, the conventional screen printing method is relatively inexpensive in equipment and is small in the number of requiring manufacturing steps. It is, however, difficult to form fine conductor patterns, and it is extremely difficult to define the line width at less than 70 .mu.m or reduce the line pitch below 150 .mu.m. In screen printing, moreover, since the conductor pattern is printed uniformly, height difference (line height difference) cannot be formed in the pattern depending on the design requirements.
Next, the conventional intaglio printing can form fine conductor patterns with the line width of about 50 .mu.m and line pitch of about 100 .mu.m, but it is hard to form a conductor film having thickness of 5 .mu.m or more. It is therefore limited to reduce the electric resistance of the conductor.
Incidentally, to achieve a desired high density of electronic components, it may not be enough by reducing the size of conductor pattern of each layer, and it may be required to form in a laminate structure. Such laminate structure has multiple layers of sandwich structure composed of lower layer conductor pattern, insulating layer, and upper layer conductor pattern. In this case, it is necessary to form via holes for connecting the conductor patterns of upper layer and lower layer, and as the size of the conductor pattern is reduced, via holes must be also reduced in size. However, in the conventional printing methods including the printing method disclosed in the above Publication No. 4-240792, it is extremely difficult to form very fine via holes with diameter of less than 100 .mu.m. Moreover, in order to achieve reliable electric connection between the conductor patterns of upper layer and lower layer, it is needed to form an electrode (called via hole electrode) for connecting the upper layer and lower layer in the inside of the via hole. In the conventional methods, however, if fine via holes of less than 100 .mu.m in diameter be formed, it is extremely difficult to form an electrode inside of the via hole of such small size.
In the conventional intaglio printing, generally, the intaglio made of stiff material such as glass and silicon wafer is used. In this case, in the step of transferring the conductor pattern on the forming object, such as ceramic or glass substrate through a setting resin, if attempted to peel off the adhered intaglio and forming object, the intaglio is hardly deformed. Accordingly, the intaglio and forming object adhering on both sides must be peeled off, and a strong peeling force is needed. To solve this problem, a metal sheet may be used for the intaglio so that the intaglio may be flexible. Even in such a case, the pattern shape processing of intaglio (groove forming) is done by wet etching, but this etching is isotropic etching. It is hence impossible to process the intaglio of high aspect ratio necessary for forming conductor pattern of thick conductor film (that is, tall line height) for the line width.
Besides, when forming the conductor pattern by firing the pattern formed of conductive paste material on the forming object such as ceramic or glass substrate through a setting resin, the thickness of the setting resin is required to be 4 .mu.m or more. At this time, the setting resin generates combustion gas while the temperature is being raised in the firing process, and the pattern deformation occurs. As a result, in the conventional intaglio printing, the dimensional accuracy is not achieved.
On the other hand, the conductor pattern forming method making use of photolithography is effective for forming patterns of small area in a line width of several microns or less as in the semiconductor technology. However, in the formation of conductor pattern used in electronic components such as inductors, it is generally required to form a pattern of a relatively wide area. In such a case, a series of steps including vapor deposition of conductive film, application of resist, exposure, development, etching, and resist removal must be done by using large-sized equipment. As a result, the equipment becomes expensive, and the manufacturing cost increases.